单选题 The chair was a movable wonder, he loved the feeling of power and strength it gave him for so little ______.

【正确答案】 D
【答案解析】(exertion费力)。句意为：那张轮椅是一个可以活动的奇物。稍一用力，它赋予他一种力量感，对这种感觉他很喜欢。A．efforts努力；B．challenge挑战；C． exchange交流，交易。